Timekeepers are introducing a ‘leap second’, which will happen after 11:59.59 on New Year’s Eve.

So chances are you’ll be shouting ‘Happy new year!’ and clinking glasses a second too early.

How it works

Time isn’t as simple as you think (Picture: Getty)

Instead of the clocks striking 00:00.00 on January 1, they will instead record a time of 23:59.60 – with midnight arriving a second later.

Bizarrely, there’s actually a precedent for this – it will be the 27th time that the National Physical Laboratory (NPL) has introduced a leap second since 1972.

Technically, the institution based in London can also remove a second, though this has never happened.

In the last 34 years, we’ve had 27 seconds added (Picture: Getty)

The science behind it

Leap seconds are needed to compensate for a slight slowdown in the Earth’s rotation.

The NPL introduces them to ensure the time, which is based on the planet’s rotation, does not lag behind the time kept by atomic clocks.

Changes in the speed of the Earth’s rotation are unpredictable, making extra seconds occasionally necessary.

Peter Whibberley, senior research scientist with NPL’s time and frequency group, said: ‘Atomic clocks are more than a million times better at keeping time than the rotation of the Earth, which fluctuates unpredictably.

‘Leap seconds are needed to prevent civil time drifting away from Earth time. Although the drift is small – taking around 1,000 years to accumulate a one-hour difference – if not corrected it would eventually result in clocks showing midday before sunrise.’

Leap seconds are usually added every two or three years, but the last one happened in June 2015.